1. Field of the Invention
The present invention relates to a super-high-speed switching device using a field-emission type cold cathode.
2. Description of the Prior Art
Research and development have been made recently on super-high-speed switching devices using a thin-film field-emission type cold cathode having the structure shown in FIG. 1 or on super-high-speed transistors. Insulation layer 22 is formed on the surface of silicon substrate 21, while gate electrode 24 having a hole 26 of 1-1.5 micrometer diameter and adjacent collector electrode 25 are formed on the insulation layer 22. During the making of hole 26, insulation layer 22 partly remains in a shape of a cone, and thereafter, a cone-shaped field-emission type cold cathode (hereinafter referred to as an emitter electrode) 23 is formed on the surface of silicon substrate 21. Accordingly, the emitter electrode 23 and the silicon substrate 21 are electrically connected. There is a 0.5-1 micrometer spacing and a 10-20 micrometer spacing provided between the tip of emitter electrode 23 and the gate electrode 24 and between emitter electrode 23 and collector electrode 25, respectively.
When the switching device is placed in vacuum and 80-100 V is fed to the gate electrode 24 with respect to the voltage of emitter electrode 23, more than 10.sup.7 V/cm of a high electric field is generated at the tip of the emitter electrode, thereby emitting electrons from emitter electrode 23, as shown by the dotted lines. The emitted electron beam enters into the collector electrode 25 so that the collector electrode 25 generates an electric signal relative to the emitted electron beam. An electron beam containing several-tens of electron volts of energy travels through a vacuum at 5-10.times.10.sup.8 cm/second of speed. This is faster than the 5.times.10.sup.7 cm/second of the maximum travel speed of an electron inside of a semiconductor by more than one order of magnitude. Accordingly, it is possible to provide a super-high-speed switching device having a switching speed faster than the switching speed of semiconductor devices, such as FETs, by more than one order of magnitude.
Although the switching device according to the prior art is capable of operating at a speed faster than that of the semiconductor switching device by more than one order of magnitude, there is a limit in the shortening of the operation time, because the prior art switching device has such a structure that the gate electrode 24 is inserted between the emitter electrode 23 and collector electrode 25. In other words, it is quite difficult according to the prior art switching device to make the spacing between the emitter electrode and the collector electrode less than 10 micrometers to shorten the electron-travel time.
Also, the rate of the electrons entering into the collector electrode is not always sufficient. Also, there is a defect in that the electron beam flows into other neighboring switching devices to cause crosstalk.
Furthermore, after forming the gate electrode and the collector electrode, it is necessary according to the prior art switching devices to go through complicated manufacturing processes such as making of a hole through the insulation layer 22 in order to form the cone-shaped emitter electrode by obliquely adhering vaporized high-melt-point metal like tungsten for example while rotating the entire substrate.